SK278148B6 - Method of mixed combustion of coal and device for realization of this method - Google Patents

Abstract

By method of mixed combustion of coal in combustion of fluid and powder combustion, is into fluid combustion chamber forced the fluidizating air with flow velocity higher than 4 m/s and into powder combustion chamber is blown the mixture of air and coal powder with flowing speed 15 to 25 m/s. Device consists of fluid combustion chamber (11) and over it is arranged the powder combustion chamber with common fireplace (2). Into space of fluid combustion chamber (11) is orificed the first coal pipe (18) or second coal pipe (19) with coal supply from first coal mill (10) and first or second air pipe (9,16) for supply of fluidization air. Powder combustion chamber is equipped with at least one torch (6), connected with leading of combustion air and with blowing pipe (5) for blowing mixture of air and coal powder leaded from second coal mill (1).

Description

The invention relates to a mixed coal combustion method and to an apparatus for carrying out the method, in a combination of fluidized-bed and pulverized-bed combustion, in a combination of a fluidized bed furnace with coal feed and a pulverized furnace with coal feed.

BACKGROUND OF THE INVENTION

In known methods and apparatuses for burning coal powder, the coal powder, ground to the desired fineness and dried in the apparatus for its preparation, is fed to a powder burner, where it is mixed with the combustion air. The mixture of coal powder and air is then ignited in the furnace and burned at high temperature. Some of the heat released is radiated through the cooling walls of the furnace while some are used on other boiler surfaces, such as a steam superheater, feed water heater, air heater.

This known method of burning coal powder and the apparatus for carrying it out are disadvantageous for several reasons. One disadvantage is that the coal must be ground to the required fineness in order to nearly completely burn the combustible proportion of the coal powder, which is associated with considerable energy consumption and cost. In spite of the measures, problems of ignition and flame extinguishing must be taken into account when the quality of the charcoal burned is lower than the expected quality. A further disadvantage is that the possible partial load, without gas or oil afterburner, is only about 60 to 70% of the rated load. It should also be considered as a disadvantage that, due to the high temperature generated in the furnace, the emissions of substances, particularly ΝΟ _χ , which are harmful to the environment, have very high values and that the additional alkalis used to bind SO2 are not efficient enough, make costly additional flue gas cleaning.

In the known fluidized bed combustion solutions, unground coal is supplied to the furnace, for example by means of an air distributor ensuring uniform distribution and is burned wholly or partially at a relatively low temperature of 750 to 950 ° C by combustion air flowing through the air distributor. In this case, the grinding of the coal powder is eliminated, thus saving costs. The high mass of the glowing fluidized bed is insensitive to changes in the quality of the burned coal and the combustion temperature in the range of 750 to 950 ° C results in limited environmental pollution by ΝΟχ and SO 3. However, the known fluidized bed combustion solutions also have certain disadvantages. In one embodiment of the fluidized bed combustion, complete combustion of the coal in the fluidized bed is achieved and the bulk of the released heat is removed by cooling surfaces immersed in the fluidized bed. In a second embodiment, the coal in the fluidized bed is only partially combusted and the gases exiting the fluidized bed are combusted with air supplied above the fluidized bed. In this embodiment, the cooling surfaces immersed in the fluidized bed are mostly omitted.

The flow rate of air supplied to properly maintain the fluidized bed and to support the combustion process is relatively low in both cases, usually less than 4 m / s. Therefore, a relatively large cross-section of the fluidized bed must be selected in a direction perpendicular to the direction of air flow compared to the dimensions of the coal powder incineration plant at which the feed rate of the coal powder and air mixture usually does not exceed 15 m / s. In other words, a relatively small amount of heat can be released per unit area of the air distributor, resulting in a considerable increase in the fluidized bed dimensions.

In order to at least partially eliminate the drawbacks and disadvantages of the fluidized bed combustion method, respectively. In the conventional combustion of coal powder, mixed combustion methods have been developed combining both methods. However, the known apparatuses for carrying out this method do not allow the necessary significant power control often required, moreover, the same sensitivity to coal quality remains as before, since the apparatuses for both combustion methods are operated by the same coal grinding and transport device, even though the apparatus comprises separate units. A typical example of such a mixed combustion is given in HU 185 694. In this apparatus, the relatively homogeneous and coal-dried pre-grits, with a certain grain size, for example 1 to 3 mm, separated in an air separator downstream of the coal mill do not return the coal mill for further fine grinding, but fed by mechanical conveying means to the fluidized bed formed at the bottom of the boiler furnace, while the finely ground coal powder which has passed through the air sorter is fed through a powder pipe to the coal powder burner where the burner opens into the fireplace. In this solution, such a coal mill is used. such an air separator that passes through the entire amount of coal required for both combustion processes. A further disadvantage of this solution is that the proportion of coal burnt in the fluidized bed and the powder burner is fixed and the operation of the fluidized bed and the burner cannot be separated from each other.

SUMMARY OF THE INVENTION

The purpose of the invention is to combine the advantages of known solutions and to eliminate their disadvantages. This is achieved by a mixed coal combustion method in combination with fluidized-bed and pulverized combustion, in combination of a fluidized bed furnace with a coal feed and a pulverized furnace with a coal-fired feed, according to the invention. 4 m / s and a mixture of air and coal powder with a flow velocity of 15 to 25 m / s are blown into the powder furnace and a mixed coal combustion plant consisting of a fluidized-bed coal-fired furnace and a coal-fired furnace a furnace for both furnaces, wherein at least one coal pipe for coal supply and at least one air pipe for fluidising air are provided in the fluidized bed space, the powder furnace being equipped with at least one burner connected to the combustion supply In accordance with the invention, it comprises a first coal line or a second coal supply line which are connected to a first coal mill which is connected to a common flue gas return line by means of a first flue gas return line. by means of a furnace, where a first coal charging device is introduced into the first flue gas return line, with the air and coal powder mixing line being connected

A second coal mill equipped with an air classifier, wherein the second coal mill is a second flue gas return line connected to a common focus, wherein a second coal charging device is introduced into the second flue gas return line. In one example of a particular embodiment, the supply of coal to a fluid feeder is driven into the fluidized bed space with a drive separate from the drive of the first coal mill. In another example of a particular embodiment, a coal powder feed from an external source, in particular a central coal mill, is driven into the powder furnace, with the drive separate from the drive of the second coal mill. An air distributor is provided at the bottom of the fluidized bed, the air distributor comprising at least two sectors, each of which is provided with separate air supply control. The width of the fluidized bed is smaller than the width of the powdered bed and the width of the common focus.

Advantage of the method and apparatus for mixed coal combustion according to the invention, wherein the space above the fluidized bed is used for the combustion of combustible gases exiting the fluidized bed, respectively. The fluidized bed, and the space for combusting the coal powder is common, is that the part of the apparatus designed to carry out the fluidized bed combustion of coal and the part of the apparatus designed to carry out the combustion of coal powder are independent of each other. Using the method and apparatus of the present invention, it is possible by partial combustion in a conventional powder furnace and partial combustion in a fluidized bed that the amount of coal combustible throughout the plant can be several times the amount of coal that can be maintained in the fluidized state by the air distributor. firebox. In the case of inferior coal quality, there are no ignition problems or unwanted flame extinguishing, since these problems are eliminated by the continuous combustion process in the fluidized bed of the fluidized bed, above the air distributor. The mixed-combustion plant is also capable of operating at a partial load of 30 to 40%, without the need for additional gas or oil heating. The temperature generated in the furnace is in the region between the values of the usual temperatures obtained in the case of powder and fluidized combustion, so that an environmentally favorable result can be achieved in comparison with powdered combustion. Care must be taken that the flame of the coal-burner does not come into contact with the opposite wall in any case, as this could eventually lead to the formation of slag or slag. to her falling. For this reason, it is expedient to select a high fluidizing air velocity higher than 4 m / s and further attenuate the flame of the coal powder burner. At the same time, the excess air of the fluidized bed operating with a large excess of air can be consumed with the coal powder blown by the powder burner, in particular at a velocity of 15 to 25 m / s, the secondary air being supplied at a reduced rate and reduced speed or completely stopped. It is preferred that the homogeneous temperature distribution in the furnace be combined with known elements or other inventions that promote the internal circulation of gas and powder. Conventional solutions can be used for admixing alkaline additives to reduce SO2 emissions that are harmful to the environment. Compared to the coal used in the powder furnace, the coal supplied to the fluidized bed may vary in terms of both quality and origin, thereby increasing the adaptability of the combustion apparatus to the particular conditions. At a lower load, the bulk of the fluidized bed furnace is operated. The combustion capacity of the powder furnace is usually chosen greater than the capacity of the fluidized bed. Therefore, the width of the fluidized bed is usually less than the overall width of the common focus. The main advantage of the mixed combustion method and apparatus is that the part of the fluidized bed apparatus can also be operated separately, i.e., without operating the part of the apparatus located above the fluidized bed furnace for pulverized coal combustion, and also vice versa equipment designed to burn pulverized coal while the fluidized bed is completely out of operation. The possibility of this independent operation increases the flexibility of the entire device, which can thus adapt to the required instantaneous power and varying fuel quality.

Overview of the figures in the drawing

BRIEF DESCRIPTION OF THE DRAWINGS The invention will be explained in more detail with reference to the drawing, in which FIG. 1 is a schematic representation of the construction of the device according to the invention; FIG. 2 shows a sectional coal mill with an air sorter; 4a and 4b show a cross-section of the fluidized bed air distributor in two different views, and FIG. 5 shows a cross-section of the flow feeder.

DETAILED DESCRIPTION OF THE INVENTION

The mixed coal combustion apparatus of Fig. 1 comprises a common focus 2, in the lower part of which a fluidized bed combustion coal 11 is arranged, above which an unlabelled powdered furnace for burning coal coal is placed in the common furnace space 2 and into the fluidized bed space 11. at least one coal duct for supplying coal and at least one air duct for supplying fluidizing air, wherein the powder furnace is equipped with at least one burner 6 connected to the combustion air supply and with the air duct 5a to blow the air-coal mixture. The apparatus comprises a first coal line 18 or an expensive coal supply line 19 which is connected to a first coal mill 10, which is connected to a common focal point 2 by a first flue gas return line 12, where a first charging device 13 is introduced into the first flue gas return line. The air and coal powder blast line 5 is connected to a second coal mill 1 equipped with an air classifier 25, wherein the second coal mill 1 is a second flue gas return line 3 connected to a common focus 2 and expensive charging flue gas return line 3 is introduced. the coal device 4.

In one embodiment of the invention, a coal feed from the grate feeder 15 with a drive separate from the drive of the first coal mill 10 is connected to the fluidized bed space. In a further exemplary embodiment, a coal powder feed from an external source, in particular a central mill. with a drive separate from the drive of the second coal mill 1. At the bottom of the fluidized bed 11 there is an air distributor 8 connected to the first air duct 9 of the fluidizing air supply. The air distributor 8 consists of at least two sectors 28, each of which is provided with a separate air supply control. The width of the fluidized bed 11 is smaller than the width of the powdered bed and the width of the common focus 2.

The burner 6 is connected to an auxiliary line 7 for supplying secondary combustion air. A second air duct 16 is introduced into the common focal point 2, above the fluidized bed 11, and the fluidized bed 11 is equipped with a de-dusting pipe 17. An outlet pipe 14 is connected to the outlet of the first coal mill 10 and further connected to the first inlet pipe 18 or the second. A first additional conduit 20 for supplying the alkaline substance to the common focal point 2 is connected to the discharge conduit 14. The second additional conduit 21 for supplying the basic substance is connected directly to the common focal point 2.

Referring to FIG. 2, a second coal mill 1 with an air classifier 25 is shown in more detail. Inlet coal 22 opens into the second coal mill 1 and the expensive coal mill 1 comprises a second grinding drum 23 driven by a second drive motor 24. Above the second grinding drum 23 a sorter 25, the bottom of which is connected by the third return line 26 to the introducing line 22.

FIG. 3 shows a first coal mill 10 without an air sorter. The first coal mill 10 comprises a first grinding drum 29, driven by a first drive motor 30. At its outlet, said discharge line 14 is connected and at its inlet a first return line 12 is connected.

As shown in Figs. 4a and 4b, an air distributor 8 for the fluidized bed 11 is arranged at the bottom of the common focus 2. The air distributor 8 is expediently divided into sectors 28. In one embodiment, the air distributor 8 is divided into 8 air inlets. The second supply line 31 is connected to the fluidized bed 11 as shown in FIG. 4b.

FIG. 5 shows an example of an embodiment of the device according to the invention with a sprinkler feeder 15 which opens into the fluidized bed space.

The spreader feeder 15 is comprised of a rotating disc 33 to which a third coal conduit 32 is provided. The first coal conduit 18 is also shown.

The function of the device according to the invention will be explained in the following examples.

The fluidizing air is supplied to the fluidized bed 11 via an air distributor 8 into which air is supplied through the first air duct 9 as shown in FIG. In the embodiment shown in Figs. 4a and 4b, the air distributor 8 is expediently divided into several sectors 28, allowing sectoral regulation of the fluidizing air flow rate, whereby a favorable distribution of the flue gas flow in the common focus 2 can be achieved. The coal is fed into the fluidized bed 11 from the first coal mill 10 or coal crusher through the first coal line 18 directly, or at the bottom through the second coal line 19 via an air distributor 8. The coal is pulverized in a coarse mill 10 or in a coal shredder to form coarse grains customary for fluidized bed combustion. There is no separation of the coarse grains and their return to the first coal mill 10, above which an air separator is therefore not arranged as shown in FIG. For coarse ground coal grains mixed with flue gas and air, they are discharged from the first coal mill 10 via a discharge line 14. Said flue gas sucks a first coal mill 10 from a common focus 2 through a first return line 12 into which coarse coal is weighed by a first weighing device 13. The mixture of coal, flue gas and air is led directly from the first coal mill 10 through the first coal line 18 to the surface of the fluidized bed 11, or is passed through the air distributor 8 below the fluidized bed 11. 4b, the fluidizing air is supplied to the fluidized bed 11 via a first supply line 27 via an air distributor 8 or an expensive supply line 31 directly to the fluidized bed 11.

The expensive coal mill 1 sucks off the hot flue gas for drying the coal conveyed by the second weighing device 4 to the second return pipe 3 through the second return line 3 from the common furnace 2 through which the coal is fed to the expensive coal mill 1. In the expensive coal mill 1 the coal is ground to the desired the fineness required for burning the coal powder. The expensive coal mill 1 is therefore equipped with an air separator 25 in which the grains of coal, flue gas and air are separated from the milled grains, not ground to the desired fineness, and these separated grains are returned to the second coal mill 1 for repeated grinding to the desired fineness. As shown in FIG. 2, said coal, flue gas and air mixture is fed to a second coal mill 1 via an inlet conduit 22 downstream of the second return line 3. The mixture is further passed to an air separator 25 from which a coarse fraction of ground milli The mixture of finely ground coal, flue gas and air, which has passed through the air classifier 25, is fed through at least one burner 6 to burn the coal powder through the lance 5. The burner 6 is further supplied with secondary combustion air via an auxiliary line 7. The coal powder can also be supplied to the burner 6 from an external source, for example from a central mill, independently of the second coal mill 1 with an air sorter 25.

In one embodiment, the coal is fed to the fluidized bed layer 11 by a feed feeder 15 as shown in Fig. 1a. Coarse coal at the desired grain size is fed through a third coal line 32 to a rotating coil 33 to disperse the coal onto the fluidized bed. In the operation of the spreader feeder 15, the first coal line 18 supplying coarse grain coal from the first coal mill 10, without an air separator, to the surface of the fluidized bed fluidized bed layer 11 is usually removed. 18, the pouring feeder 15 is usually disabled.

In all of these embodiments, the amount of air supplied to the second air duct 16, together with the supply of secondary combustion air through the auxiliary duct 7, is necessary to completely burn the gas / flue gas mixture exiting the fluidized bed combustion chamber 11a. The gas / flue gas mixture exiting the fluidized bed space 11 is adjusted to the usual value of 2 to 10%. The temperature in the fluidized bed 11 is controlled by controlling the amount of fluidizing air supplied. The common focal point 2 is fed with a first additional line or a second additional line 21 with an alkaline substance which binds the resulting SO ₂ , polluting the environment. After the combustible portion of the feed coal has been burned, the non-combustible solids are discharged from the common focus 2 through the de-deburring line 17, led through the air distributor 8 and into the corresponding de-deburring device.

When considering the separate operation of a portion of a fluidized-bed plant, i. without operating the part of the coal-fired furnace, the second weighing device 4 and the second coal mill 1 are disabled, and the blowing pipe 5 does not inject the coal powder into the burner 6, while the first weighing device 13, the first coal mill 10 or the feed feeder 15 supplies the fluidized-bed part of the apparatus. Conversely, when the coal-fired part of the apparatus is to be operated without commissioning the fluid-fired part of the apparatus, a second coal mill 1 and a blast pipe 5 conveying the coal powder are in operation, while the first weighing apparatus is operated. 13, the first coal mill 10 or the gripper 15 and the first air duct 9 are taken out of operation.

As is clear from the above description of the embodiment, the mixed coal combustion method and the apparatus for carrying out the method enable the combination of pulverized and fluidized bed combustion, while eliminating the drawback of both methods and apparatus. An essential advantage of the method and apparatus according to the invention is that even with less valuable or poor quality of the coal to be burned, it can still be combusted even at partial load to 30-40%, while the amount of heat released from the common focus 2 is not limited at all. 8 and thus environmental benefits can be achieved.

These disadvantages also occur when converting conventional coal powder boilers to a mixed combustion plant according to the invention. The conversion of a boiler originally designed for pulverized combustion is effected by removing the air sorter 25 from the part of the second air mills 1 with air sorter 25 intended for grinding fine powder, thereby converting the second air mills 1 with air sorter 8 to the first coal mill 10 without air sorter. Instead of the bottom hopper, a fluidized bed 11 is formed to which coarse-grained coal from this treated first mill is supplied.

10. An air distributor 6 is provided below the fluidized bed 11 for supplying fluidizing air to the fluidized bed 11. The remaining coal mills for grinding fine coal powder as well as the powder burners can remain unchanged.

Such a conversion of the boiler is particularly advantageous when the quality of the coal to be burned changes and deteriorates, and the steady operation of a better coal-fired boiler with the initially built-in coal powder combustor cannot be properly maintained. After conversion, continuous operation is also ensured by fluidized-bed combustion, even if the quality of the coal is inferior, the main components need not be changed.

Claims (7)

1. A method of mixed coal combustion in a combination of fluidized-bed and pulverized combustion, in a fluidized bed coal-fired furnace and a coal-fired powder furnace, characterized in that fluidizing air is blown into the fluidized bed at a flow rate greater than 4 m / s. A powder mixture of air and coal powder with a flow rate of 15 to 25 m / s is blown. An apparatus for carrying out the method according to claim 1, comprising a fluidized bed coal combustion furnace and a pulverized coal fired furnace arranged above it, with a common focus for both furnaces, wherein at least one coal pipe for the coal supply is connected to the fluidized bed space. one air duct for supplying fluidizing air, the powder furnace being equipped with at least one burner connected to the combustion air supply and with an air duct for air / coal powder blowing, characterized in that it comprises a first coal duct (18) or a second coal duct (19) ) for the supply of coal connected to a first coal mill (10) which is connected by a first flue gas return pipe (12) to a common focus (21) for a fluidized bed (II) and a powder furnace, where flue gas is introduced first weighing device coal (13), wherein the air / coal powder blast line (5) is connected to a second coal mill (1) equipped with an air sorter (25), wherein the second coal mill (1) is a second flue gas return line (3) connected to by means of a common focus (2), wherein a second coal weighing device (4) is introduced into the second flue return pipe (3). Apparatus according to claim 2, characterized in that a coal feed from the sprinkler (15) with a drive separate from the drive of the first coal mill (10) is introduced into the fluidized bed (11). Apparatus according to claim 2, characterized in that the powder furnace is provided with an inlet of coal powder from an external source, in particular from a central coal mill with a drive separate from the drive of the second coal mill (1). Apparatus according to claim 2 or 3, characterized in that an air distributor (8) is provided in the lower part of the fluidized bed (11) and is connected to the first air supply (9) of the fluidizing air supply. Device according to claim 5, characterized in that the air distributor (8) consists of at least two sectors (28), each of which is provided with a separate air supply control. Device according to claims 2 to 5, characterized in that the width of the fluidized bed (11) is smaller than the width of the powder furnace and the width of the common focus (2).